Studies Of Integrated Etched Diffraction Grating Demultiplexers For Optical Communications

With the rapid development of information technologies, more and more bandwidth is needed for information exchange. Wavelength Division Multiplexing (WDM) is a very effective technique to meet the fast-growing demand for the communication capacity. A demultiplexer is the key device in a WDM system. Among all kinds of demultiplexers, Etched Diffraction Gratings (EDGs) are regarded as one of the most potential types of planar waveguide WDM devices.This PhD thesis focuses on the design, simulation and fabrication of EDGs for optical communications. The basic theory of the EDG and the design principle are analyzed here, and the essential experience and methods in the EDG design are given. To simulate the performance of the device and to reduce the possibility of failure in the fabrication of a device sample, we present a relatively accurate method for the simulation of an EDG. Based on this simulation method, the following novel designs are developed:1, The two-stigma design, which can reduce the aberrations and improve the imaging of the grating;2, The flat-field design, which can omit the output waveguides and make an EDG easier tc fabricate;3, The passband flattening design, which can relax the requirements on wavelength control for lasers and filters in a WDM system;4, The reduced back-reflection design, which guarantees very little reflection light back into the input channel and improves the feature of the return loss.In this thesis, all the manufacture processes are described. The processes include the deposition of the waveguide film, the design and fabrication of the mask pattern, the lithography, the metal coating with a magnetic sputtering, the lift-off process for the metal mask, the dry deep etching by ICP, the slicing of the wafer, the polishing of the cutting edge, the fiber-to-waveguide alignment and at last, the performance testing. Some EDG chip samples are fabricated.Among the manufacture processes, this thesis focuses on the deposition of silica waveguidi film with a Plasma Enhanced Chemical Vapor Deposition (PECVD). The waveguide is the basis for integrated optical devices and its optical properties affect greatly the performances of the device. A lot thin film depositionexperiments have been carried out and the optimal condition for the deposition is obtained.